It is still possible to find great bargains on Ebay. Much less than it used to be, unfortunately.
About ten years ago I found on Ebay Italy the second most valuable lens I own.
A second hand shop could not sell locally a Kodak 4x5" monorail camera. The same model that was later sold as Calumet.
It had a nice iris shaped lens holder (a device that clamps non standard shutter-less objectives to the lens board of the camera), a Schneider Symmar 135mm convertible (the last double anastigmat, both cells give a very corrected image, the rear cell alone can be used as a portrait lens), and a nice, huge brass lens that seemed to be badly affected by a leak of some corrosive fluid.
I bought everything for 100 euros, Buy It Now.
The camera went to a young photographer who wanted to start with large format. I sold it for 70, a great deal for him cause the camera was complete of everything and like new.
I still have the lens holder (they go for about 200), and the Symmar (it had a broken shutter and was repaired by a friend, even after a CLA it should fetch not more than 70/100).
The "problematic" old lens was a Cooke Portrait 270mm. I had seen the engravings in the picture and that was the real reason for my acquisition.
A very fortunate one, I'd say... cause the glasses cleaned perfectly, the softness ring was smooth again, and the barrel, after removing the oxidised gunk, just exposed the shiny brass surface underneath. Now the only visible problem is a small part of the barrel that looks shinier and lighter than the rest (covered by the original lacquer).
Some "french lacquer", the same used to restore old furniture, would make the discolouration almost invisible. In the meantime, the brass has oxidised a little, so it's barely visible.
I am glad I bought it, the problem the lens had proved to be minimal, and even with a little discolouration it's very valuable.
It's the Series IIE. The only model of the Cooke Portrait lenses with adjustable soft focus ever made with coated glasses. AFAIK all the others are uncoated.
The value of the lens is secondary, probably I will never sell it. I'm not actively collecting large format lenses anymore, but it's very likely that those I own will stay with me for a long long time
What is more relevant in this little story is its value as a practical example.
With some patience, some knowledge, and some spare time to dedicate to searches (trying to use smart keywords), it was possible, and it's still possible to score very nice deals.
In this case the most valuable element of the bundle was not mentioned in the description, nor in the accompanying text.
Typos, bad or missing descriptions, wrong categories are all possible sources of unexpected strokes of luck.
Doing your home work first, which means knowing what you want to buy and why, is usually a necessary precondition.
Fortunate acquisitions don't usually fall on your lap. It takes some effort.
Better not forget any possible source. I have seen auctions end at higher prices than Buy It Now alternatives, in the same (if not better) conditions.
My most valuable lens, a Voigtlander prototype of an inverted Petzval, was bought from the biggest german photographica shop on Ebay.
They couldn't open it, and it was sold as no-name projection Petzval. I offered 100 euros and they accepted.
It took A LOT of effort to open it, and plenty of gentle hammering, and when I could unscrew the elements, I found inked on the rim of two glasses, the source of the objective:
"Voigtlander & Sohn, Wien und Braunschweig". Which means made by Voigtlander before 1862/63.
The layout, completely different from any other Voigtlander Petzval, reveals that it was a prototype. I asked the authors of two books on Voigtlander history, they never saw another one. It is really a reversed Petzval, and not a wrongly reassembled one, because the threads are different, and there is one, and only one way to assemble the glasses.
So my two most valuable lenses were purchased for 100 euros each
With modern lenses I was less fortunate. Two very expensive Sigma AF zooms were not tested in time (I had it shipped to a friend, and I picked them up months later), and both had bent zoom or/and focusing sleeves. I ended up paying almost as much as buying them new
One last thing.
I already wrote a post about this issue. Maybe it's worth repeating the concept.
Please use some restraint.
Some Ebay vendors are consistently overpricing their cameras/lenses.
If they do, I am sure it's because somebody buys them.
Avoiding overpriced items doesn't just do a big favour to your wallet, it is also affecting the "market".
The price dynamics are affect by (collective) consumer's behaviour.
The whole set of Pentax enthusiasts is not extremely huge. A relatively small number of individuals can impact this kind of dynamics.
Even more so if these individuals are seen as "influencers" by a larger set of people. Some youtubers have a huge number of followers, and those followers actually buy stuff....
Instead of preaching brand loyalty (others do it much better than I could), I prefer to humbly suggest restraint.
Pentaxians don't necessarily have to pay an extra for their choice. I find it very difficult to stomach.
One example: I really want the Voigtlander/Cosina 40mm and 90mm in PKA mount. Though when I look for one I always find prices that IMHO are way too high.
If the same lens sells for as low as 250 USD in Nikon mount, I don't see how a Pentax version should cost 450/500 dollars.
Of course it's less common, but the difference is embarrassing. I mean, I would feel seriously embarrassed if I bought at those prices, even if money was no concern.
Your mileage may vary, even by a whole lot.... just expressing an opinion and suggesting a touch of moderation that would ultimately benefit all of us